Solder Ball Loading Mask, Apparatus And Associated Methodology

ABSTRACT

A solder ball loading method capable of securely loading solder balls on connection pads includes applying flux on each connection pad group of a printed wiring board flux is not applied to a contact portion between a spacer and the printed wiring board to keep the flux from attaching to the spacer. Because the flux is not attached to the spacer, when the mask is detached from the printed wiring board, the printed wiring board need not be inverted, and damage to the solder resist layer  70  is minimized. Further, the heights of the solder balls and the upper surface of the mask are made equal by using the spacer, making it possible to securely load the solder balls on the electrode pads, one solder ball for each connection pad, and to reduce a probability that solder balls are not loaded or that a plurality of the solder balls are loaded onto a single connection pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofpriority to U.S. application Ser. No. 12/349,748, filed Jan. 7, 2009,which claims the benefit of priority to U.S. Provisional Application No.61/057,479, filed May 30, 2008. The contents of these applications areincorporated herein by reference in their entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a solder ball loading method forloading a solder ball onto a printed wiring board. The solder ball is tobe made into a solder bump.

2. Background Art

Solder bumps are used for electrical connection between a printed wiringboard and an IC chip. The solder bumps are formed through a process ofprinting a flux on a connection pad formed on a printed wiring board, aprocess of loading a solder ball on the connection pad with the fluxprinted thereon, or a process of forming a solder bump from the solderball by performing reflow.

In the aforementioned process of loading the solder ball on the printedwiring board, a mask having openings for dropping the solder ball on theprinted wiring board is used. The mask includes a spacer, formed from aplurality of protrusions, such that when the solder balls are loaded onthe printed wiring board, the mask is aligned with the printed wiringboard the protrusions are disposed between adjacent electrode portions.Japanese Patent Application Publication No. 2006-324618, the entirecontents of which are incorporated herein by reference, is an example ofthis process.

SUMMARY

One aspect of the invention is a solder ball loading method for loadinga solder ball on connection pads of a printed wiring board. The methodincludes applying a flux on a surface of the connection pads of theprinted wiring board. Then the method includes preparing a mask that hasa mask main body with a plurality of openings that correspond to theconnection pads. The mask also includes a spacer whose opening portioncorresponds to the plurality of openings on the mask main body. Theplurality of openings on the mask main body are aligned to face theconnection pads of the printed wiring board, and a solder ball issupplied to the mask. The solder ball is dropped on the connection padthrough one of the plurality of openings of the mask main body.

Another aspect of the invention is a solder ball positioning mask. Thesolder ball positioning mask includes a mask main body that has aplurality of openings corresponding to a plurality of connection pads ona printed wiring board. The solder ball positioning mask also includes aspacer whose opening portion includes the plurality of opening on themask main body.

A further aspect of the invention is a solder ball loading apparatus.The solder ball loading apparatus has a table that is movable in avertical direction, and supports a printed wiring board. A solder ballpositioning unit that positions a solder ball according to a solder ballpositioning mask, and a solder ball removal tube removes excess solderballs from the solder ball positioning mask. A first airflow unit causesan airflow into the solder ball removal tube. The solder ballpositioning mask included in the solder ball loading apparatus has amain body with a plurality of openings for transporting the solder ballto a connection pad of the printed wiring board. A spacer, whose openingportion encompasses the plurality of openings in the main body, alsoforms part of the solder ball positioning mask.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a rear view illustrating a mask according to an exemplaryembodiment of the present disclosure,

FIG. 2 (A) is a plan view of a mask main body,

FIG. 2 (B) is a plan view of a spacer,

FIG. 3 is a plan view of a multilayer printed wiring board for gangprinting where solder balls are loaded by using a mask according to anexemplary embodiment of the present disclosure,

FIG. 4 (A) is a view corresponding to a cross section A-A of FIG. 1,

FIG. 4 (B) is an enlarged view illustrating a portion indicated by acircle b in FIG. 4 (B),

FIG. 5 is a schematic view of steps of a method for manufacturing a maskaccording to an exemplary embodiment of the present disclosure,

FIG. 6 is a schematic view of a step of fixing the mask on a frameaccording to an exemplary embodiment of the present invention,

FIG. 7 (A) is a schematic view of loading solder balls using the maskaccording to an exemplary embodiment of the present disclosure,

FIG. 7 (B) is a schematic view of loading solder balls according to amodified example of an exemplary embodiment of the present disclosure,

FIG. 8 is a schematic view of a mask according to an exemplaryembodiment of the present disclosure,

FIG. 9 (A) is a schematic view of loading solder balls using a maskaccording to an exemplary embodiment of the present disclosure,

FIG. 9 (B) is a schematic view of loading solder balls according to amodified example of the exemplary embodiment of the present disclosure,

FIG. 10 (A) is a schematic view of loading solder balls using a maskaccording to an exemplary embodiment of the present disclosure,

FIG. 10 (B) is a schematic view of loading solder balls according to amodified example of the exemplary embodiment of the present disclosure,

FIG. 11 (A) is a schematic representation of a solder ball loadingapparatus according to an exemplary embodiment of the presentdisclosure,

FIG. 11 (B) is a schematic representation of the solder ball loadingapparatus as seen from an arrow B of FIG. 11 (A),

FIG. 12 (A) is a schematic view of alignment of a multilayer printedwiring board,

FIG. 12 (B) is a schematic view of supplying solder balls to a loadingtube,

FIG. 13 (A) is a schematic view of collecting solder balls using aloading tube,

FIG. 13 (B) is a schematic view of collecting and inducing solder ballsusing a loading tube,

FIG. 14 (A) is a schematic view of dropping solder balls on connectionpads,

FIG. 14 (B) is a schematic view of removing solder balls using aabsorbed ball removing tube,

FIG. 15 (A) is a schematic view of a process for manufacturing amultilayer printed wiring board,

FIG. 15 (B) is a schematic view of processes for manufacturing amultilayer printed wiring board,

FIG. 15 (C) is a schematic view of processes for manufacturing amultilayer printed wiring board,

FIG. 16 is a cross-sectional view of a multilayer printed wiring board,

FIG. 17 is a cross-sectional view of an IC chip attached on themultilayer printed wiring board, illustrated in FIG. 16, that is mountedon a daughter board,

FIG. 18 is a plan view of a multilayer printed wiring board for gangprinting, and

FIG. 19 is a schematic view of dropping solder balls when a height ofsolder balls is larger than that of a mask.

DETAILED DESCRIPTION

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

An object of the present invention is to provide a solder ball loadingmethod capable of securely loading solder balls on connection pads. Inorder to achieve this objective, the invention provides a solder ballloading method for loading a solder ball on connection pads of a printedwiring board. The method also includes applying a flux on a surface ofthe connection pad of the printed wiring board. A mask including a maskmain body and a spacer is prepared. The mask main body has an openinggroup including a plurality of openings corresponding to the connectionpads, and the spacer has an opening portion exposing the opening group.The mask is aligned with the printed wiring board so that the openingsof the mask main body face the connection pads of the printed wiringboard, and the solder balls are supplied to the mask and dropped on theconnection pad through the openings of the mask main body.

In the solder ball loading method according to the present invention,the flux can be applied over all of the connection pad formation regionsof the printed wiring board. This simplifies the manufacturing processwhen compared to a case where the flux is locally applied on each of theconnection pads. In addition, since the flux is applied to the entireregion, no connection pad is missed, and it is possible to securely loadthe solder ball on each of the connection pads.

In addition, the spacer and the mask main body are integrally formed,making accurate control of the height of the mask possible in order toequalize the heights of the solder balls and the upper surface of themask. Accordingly, it is possible to securely load the solder balls onthe connection pad, and to reduce a probability of that solder balls arenot loaded on their respective pads or that a plurality of the solderballs are loaded on a single connection pad.

First Embodiment

A mask for loading solder balls on a printed wiring board according to asolder ball loading method of a first exemplary embodiment is describedwith reference to FIGS. 1 through 7.

FIG. 3 is a sheet-sized printed wiring board 10 having solder ballsloaded thereon using a mask according to a first exemplary embodiment.For example, the sheet-sized printed wiring board 10 is a printed wiringboard for gang printing in order to manufacture 4×4 inch-sized printedwiring boards 10R. In the figure, 16 printed wiring boards 10R cut alongdotted lines Z are manufactured in the sheet-sized printed wiring board10. A connection pad formation region 75 g is disposed in a centralportion of each printed wiring board 10R. A plurality of connection pads75 for loading solder balls are formed in the connection pad formationregions 75 g. Each connection pad formation region 75 g denotes aspecific region having a minimum area large enough to encompass theentire connection pads of the printed wiring board 10R.

FIG. 1 is a schematic view of a mask 80 used to load solder balls on theprinted wiring board of FIG. 3. The mask 80 includes a mask main body 82having opening groups 84 g that include openings 84 corresponding to theconnection pads 75 of the printed wiring board 10. A spacer 86 is formedwith opening portions 86 a for exposing the opening groups 84 g of themask 80, and the mask main body 82 and the spacer 86 are integrallyformed. In this context, the term “integrally” includes formation of thetwo members by the same process, formation of the two members with thesame material, and separate fixation of the two members. For example,FIG. 2 (A) is a plan view of the mask main body 82, and FIG. 2 (B) is aplan view of the spacer 86.

FIG. 4 (A) corresponds to a cross section A-A of FIG. 1, when the mask80 is loaded on the printed wiring board 10, and FIG. 4 (B) is anenlarged view of a portion indicated by circle b in FIG. 4 (A). A solderresist layer 70 is formed on a surface of the printed wiring board 10,and the connection pads 75 are exposed by openings formed on the solderresist layer 70. The flux 79 is applied on the entire connection padformation region 75 g of the printed wiring board 10. However, theregion where the flux is applied is smaller than the opening portion 86a of the spacer 86. Thus, in the printed wiring board 10, the flux 79 isapplied on the connection pad formation region 75 g except for portionsthat are in contact with the spacer 86.

In the first exemplary embodiment, the flux 79 is applied on theconnection pad formation region 75 g except for the contact portionsbetween the spacer 86 and the printed wiring board 10. Since the flux isnot applied to the spacer 86, when the mask 80 is detached from theprinted wiring board 10, a probability of defects, such as warping ofthe printed wiring board, misalignment of solder balls on the connectionpad, and damage to the solder resist layer 70 is reduced.

As shown in FIG. 4 (B), a thickness of the mask 80 is designed so that,when the solder balls 78 are loaded on the connection pads 75, a heightof the upper surface of the mask 80 and a height of the vertexes of thesolder balls 78 are substantially equal to each other. For example, whenthe solder ball 78 has a diameter B of 70 μm, a thickness h1 of the maskmain body 82, a thickness h2 of the spacer 86, and a thickness h3 of thesolder resist layer from the connection pad 75 are designed to be 25 μm,30 μm, and 15 μm, respectively. In this context, the “vertex of thesolder ball” denotes a portion of a surface of a solder ballcorresponding to the maximum height of the solder ball.

According to the solder ball loading method of the first exemplaryembodiment, the vertexes of the solder ball 78 are substantially flushwith the upper surface of the mask 80, so that a predetermined amount ofsolder balls can be securely loaded on the electrode pads 75 at a rateof one solder ball per electrode pad 75. In addition, it is possible toreduce a probability that solder balls are not loaded on every electrodepad or that a plurality of the solder balls are loaded on a singleelectrode pad. In FIG. 19, when the height of the upper surface of themask 80 is higher than the height of the solder ball 78, other solderballs may be loaded through the openings of the mask main body on top ofthe solder balls already loaded on the connection pads. A case where thesolder balls protrude from the upper surface of the mask 80 is notpreferable because loading of solder balls on other connection pads maybe difficult, and upon reflow, solder bumps having volumes exceeding apredetermined volume (for example, the volume of a single solder ball)may be formed, possibly reducing yield.

In addition, it is preferable that a diameter of the opening of the maskmain body be 1.2 times to 1.5 times larger than a diameter of a solderball. For example, in a case where solder balls having a diameter of 70μm is used, the diameter of the opening of the mask main body ispreferably in a range of 84 to 105 μm to ensure that the solder ballscan be securely loaded on the connection pads. A diameter less than 1.2times the solder ball diameter may prevent the solder balls from beingloaded on the connection pads, and a diameter more than 1.5 times thediameter of the solder ball may increase a probability that a pluralityof solder balls are loaded on a single connection pad.

FIG. 7 (A) is a schematic view of loading solder balls using the mask 80according to the first exemplary embodiment. A tube member 24 having anopening portion 24A facing the mask 80 is positioned over the mask 80.Air is absorbed through the tube member 24, to collect the solder balls78 on the mask that are disposed just under the tube member 24. The tubemember 24 is then moved in a horizontal direction relatively to the mask80. Accordingly, the collected solder balls 78 are moved on the mask 80and dropped on the connection pads 75.

FIG. 7 (B) is a modified example of the first exemplary embodiment. InFIG. 7 (A), the air is absorbed by the tube member 24. However, in themodified example of FIG. 7 (B), the air is ejected from the tube member24, and thus, the solder balls 78 are dropped on the connection pads 75.

According to the solder ball loading method of the first exemplaryembodiment, a tube member 24 is disposed over the mask 80, and air isabsorbed through an opening portion of the tube member 24 to collectsolder balls 78. The tube member 24 is then moved in a horizontaldirection, to move the collected solder balls 78 on the mask 80.Accordingly, the solder balls 78 are dropped on the connection pads 75through the opening 84 of the mask. Therefore, fine solder balls can besecurely loaded on all of the connection pads of the printed wiringboard. Since the solder balls are moved without physical contact, unlikethe case of using a squeegee, the solder balls can be loaded on theconnection pads without damage, maintaining a uniform height for thesolder bumps. The solder balls can even be securely loaded on a printedwiring board having large unevenness thereon, such as a build-upmultilayer wiring board.

In the first exemplary embodiment, the portions forming the openinggroups 84 g of the mask main body 82 are supported by the spacer 86 infour directions and therefore are hardly deflected. Thus, a distancebetween the mask main body 82 and the printed wiring board 10 can beuniformly maintained. Further, the spacer 86 blocks air flow through thegap between the mask 80 and the printed wiring board 10, though air isabsorbed by the tube member 24. In addition, the distance between themask main body 82 and the printed wiring board 10 is uniformlymaintained without floating the mask main body 82 with air flow from thelower portion of the mask 80.

Next, a method for manufacturing the mask 80 of the first exemplaryembodiment is described with reference to FIG. 5.

A plating resist 202 for forming the openings 84 of the mask 80 isformed on an SUS plate 200 that is subjected to surface treatment (FIG.5(A)). In this state, the mask main body 82 having the openings 84 isformed using a nickel alloy electrolytic plating method (FIG. 5 (B)).Next, the plating resist 204 that will form the opening portion of thespacer is formed on the mask main body 82 (FIG. 5 (C)). Next, the spacer86 having the opening portion 86 a is formed using the nickel alloyelectrolytic plating method (FIG. 5 (D)). The plating resist 202 and theplating resist 204 are dissolved using a predetermined solution, andsubsequently, the mask 80, including the spacer 86 and the mask mainbody 82, is detached from the SUS plate 200 (FIG. 5(E)). In this manner,the spacer 86 and the mask main body 82 are integrally formed throughthe plating to accurately adjust thickness thereof.

In the first exemplary embodiment, the spacer 86 and the mask main body82 are integrally formed. However, the spacer 86 and the mask main body82 may also be separately formed and adhered using, for example,ultrasonic adhesion or an adhesive. Alternatively, the spacer 86 and themask main body 82 may be formed with different materials. For example,the mask main body 82 may be formed using a metal and the spacer 86 maybe formed by using a resin.

Attachment of the mask 80 to a supporting mechanism is described withreference to FIG. 6. As shown in FIG. 6 (A), the supporting mechanism isformed by adhering a nylon cloth 220 to a frame 210 with a uniformtension exerted thereon. The mask 80 is adhered at the center of thenylon cloth 220 using an adhesive 222 (FIG. 6(B)). The adhesive 222 isapplied to an outer side of the spacer 86 in the outer circumference ofthe mask main body 82. Finally, in FIG. 6 (C), the opening 220A isformed in the nylon cloth 220 in an inner side of the adhesive 222, toexert a uniform tension of the nylon cloth 220 on the mask 80.

In the first exemplary embodiment of FIG. 6 (B) and FIG. 1, an outercircumference of the mask main body 82 extends over the outercircumference of the spacer 86. Tension is exerted to the outercircumference of the mask main body 82 to exert uniform tension to aportion of the mask main body 82 where the spacer 86 is located and to aportion where the opening portion of the spacer 86 is disposed.Accordingly, uniform tension can be exerted on the entire portions ofthe mask main body 82. As a result, deflection due to tensiondifferences is suppressed, a height of the mask main body 82 can beaccurately controlled to maintain the solder ball 78 and the mask 80 atthe same height.

Second Embodiment

A mask according to a second exemplary embodiment is described withreference to FIG. 8. In the second exemplary embodiment, openingportions 86 a are formed in the spacer 86 so that a plurality of openinggroups 84 g of the mask main body 82 can be exposed through a singleopening portion 86 a.

Third Embodiment

A solder ball loading method according to a third exemplary embodimentis described with reference to FIG. 9 (A). In the third exemplaryembodiment, solder balls 78 are loaded on connection pads 75 by a brush110.

Modified Example of Third Embodiment

A solder ball loading method according to a modified example of thethird exemplary embodiment is described with reference to FIG. 9 (B). Inthe modified example of the third exemplary embodiment, solder balls 78are loaded on the connection pads 75 by using a flexible squeegee 112.

Fourth Embodiment

A solder ball loading method according to a fourth exemplary embodimentis described with reference to FIG. 10 (A). In the fourth exemplaryembodiment, solder balls 78 are loaded on connection pads 75 byvibrating the mask 80 and the printed wiring board 10.

Modified Example of Fourth Embodiment

A solder ball loading method according to a modified example of thefourth exemplary embodiment is described with reference to FIG. 10 (B).In the modified example of the fourth exemplary embodiment, solder balls78 are loaded by inclining the mask 80 and the printed wiring board 10.

Example 1

Next, a first example of the present invention is described withreference to FIGS. 11 to 17.

A construction of a multilayer printed wiring board 10 manufacturedusing a solder ball loading method according to the first example of thepresent invention is described with reference to FIGS. 16 and 17. FIG.16 is a cross-sectional view of the multilayer printed wiring board 10,and FIG. 17 is a view of an IC chip 90 attached on the multilayerprinted wiring board 10 of FIG. 16, and mounted on a daughter board 94.In the multilayer printed wiring board 10 of FIG. 16, conductor circuits34 are formed on both surfaces of a core board 30. Front and rearsurfaces of the core board 30 are interconnected via through holes 36.

In addition, a conductor circuit 58 as a conductor circuit layer isformed through an interlayer resin insulating layer 50 on the conductorcircuit 34 of the core board 30 through via holes 60. A conductorcircuit 158 is formed on the conductor circuit 58 through an interlayerresin insulating layer 150, and is connected to the conductor circuit 58through via holes 160 formed on the interlayer resin insulating layer150.

A solder resist layer 70 is formed on an outermost layer of thevia-holes 160 and the conductor circuit 158. A nickel plating layer 72and a gold plating layer 74 are disposed on the openings 71 of thesolder resist layer 70 to form the connection pads 75. The solder bumps78U are formed on the connection pads 75 of the upper surface of theprinted wiring board 10, and the solder bumps 78D are formed on theconnection pads 75 of the lower surface of the printed wiring board 10.

In FIG. 17, the solder bumps 78U on the upper surface of the multilayerprinted wiring board 10 are connected to electrodes 92 of the IC chip90, and the solder bumps 78D on the lower surface of the printed wiringboard 10 are connected to lands 90 of the daughter board 94.

FIG. 18 is a plan view of a sheet-sized multilayer printed wiring board10A for gang printing. In this context, “gang printing” refers tosimultaneously printing all printed wiring boards 10 on the sheet-sizedmultilayer printed wiring board 10A. The multilayer printed wiring board10A is divided into individual multilayer printed wiring boards 10having connection pad formation regions 75 g that include connectionpads 75 arrayed in matrix. The multilayer printed wiring boards 10 areseparated by cutting along a dotted line in the figure. FIG. 15 is aview of a process of forming the solder bumps on the multilayer printedwiring board 10A for gang printing and corresponds to a cross-sectionalview taken along line Y1-Y1 of FIG. 18. In FIG. 15 (A), the flux 79 isprinted over the entire surface including openings 71 of the solderresist layer 70 and a surface of the connection pads 75. As shown inFIG. 15 (B), fine solder balls 78S (for example, a solder ballmanufactured by Hitachi Metals, LTD., having a diameter of equal to orlarger than 40 μmΦ and less than 200 μmΦ) are loaded on the connectionpads 75 on the upper side of the multilayer printed wiring board 10Ausing a solder ball loading apparatus described below. In this case, ifthe solder ball has a diameter of less than 40 μmΦ, the solder ball istoo light to be dropped on the connection pad 75. If the solder ball hasa diameter of larger than 200 μmΦ, the solder ball is too heavy to becollected in a tube member, such as the tube member 24 of FIG. 7 (A). Ineither case, at least some connection pads may be left without solderballs. As recognized by the present inventor, it is important to usesolder balls having a diameter of equal to or larger than 40 μmΦ butless than 200 μmΦ to avoid the above-described issues. This range isuseful for fitting solder balls in openings 71 of the solder resistlayer 70 when the diameter of openings 71 have been reduced duringmanufacturing of the printed wiring board 10. In addition, since thesolder balls are small, they are difficult to absorb using an absorptionpad. Therefore, the method according to this exemplary embodiment ismore effective than conventional methods for at least these reasons.

Next, in FIG. 15 (C), solder balls 78L having a typical diameter (25 μm)are absorbed and loaded on the connection pads 75 of the lower side ofthe multilayer printed wiring board 10A using a conventional absorptionpad (for example, U.S. Pat. No. 1,975,429). The solder balls are thenheated by a reflow furnace, and in FIG. 16, for example, 500˜30000solder bumps 78U are formed on the upper side of the printed wiringboard 10A with a pitch equal to or larger than 60 μm but less than 200μm. Continuing the example, 250 solder bumps 78D are formed with a pitchof 2 mm on the lower side of the printed wiring board 10A. Manufacturingsolder balls of a pitch less than 60 μm is difficult. A pitch equal toor larger than 200 μm allows the solder balls to be manufactured withoutproblems using conventional methods, and such solder balls still suitthe present invention.

A method as described above may be used, for example, in the printedwiring board 10A of FIG. 17, where the multilayer printed wiring board10A for gang printing is divided into individual multilayer printedwiring boards 10, and the IC chip 90 is mounted through the solder bumps78U by reflow. Then, the multilayer printed wiring board 10, on whichthe IC chip 90 is mounted, may be attached on the daughter board 94through the solder bumps 78D.

A solder ball loading apparatus for loading fine solder balls 78 s(having a diameter less than 200 μm) on the connection pads 75 of themultilayer printed wiring board 10A of FIG. 15 (B) is described withreference to FIG. 11. FIG. 11 (A) is a schematic view of a solder ballloading apparatus according to the solder ball loading method of thefirst example, and FIG. 11 (B) is a schematic view of the solder ballloading apparatus of FIG. 11 (A) as seen from arrow B.

The solder ball loading apparatus 20 includes an XYθ absorption table 14for positioning and supporting the multilayer printed wiring board 10A,an up/down moving axis 12 for lifting the XYθ absorption table 14, aball alignment mask 80 having openings corresponding to connection pads75 of the multilayer printed wiring board, a loading tube (tube member)24 for inducing the solder balls moving on the ball alignment mask 80,an absorbing unit 26 for pressing the loading tube 24, an absorbed ballremoving tube 61 for recovering redundant solder balls, an absorbingunit 66 for pressing the absorbed ball removing tube 61, an absorbedball removing absorption apparatus 68 of holding the recovered solderballs, a mask clamp 44 for clamping the ball alignment mask 80, an Xdirection moving axis 40 for moving the loading tube 24 and the absorbedball removing tube 61 in the X direction, a moving axis support guide 42for supporting the X direction moving axis 40, a alignment camera 46 forphotographing the multilayer printed wiring board 10, a solder balldetection sensor 18 for detecting a remaining amount of the solder ballsbelow the loading tube 24, and a solder ball supplying apparatus 22 forsupplying the solder balls to the loading tube 24. The solder ballsupplying apparatus 22 supplies solder balls to the loading tube 24based on the remaining amount detected by the remaining amount detectionsensor 18. In the solder ball loading apparatus 20 of FIG. 11, only theX direction moving axis 40 for moving the loading tube 24 and theabsorbed ball removing tube 61 in the X direction are provided, butmoving mechanisms for moving the loading tube 24 and the absorbed ballremoving tube 61 in the Y direction may also be provided. Alternatively,the loading tube 24 may be fixed, and the side of the ball alignmentmask 80 and the printed wiring board 10A may be moved in the X and Ydirections.

FIG. 1 is a rear view illustrating the mask 80 used for the solder ballloading apparatus 20 of FIG. 11. As described above, the mask 80includes a mask main body 82 where opening groups 84 g made of openings84 corresponding to the connection pads 75 of the printed wiring board10 are formed and a spacer 86 where opening portions 86 a for exposingthe opening groups 84 a are formed. The mask main body 82 and the spacer86 are integrally formed.

FIG. 4 (A) corresponds to a cross section taken along line A-A of FIG. 1when the mask 80 is mounted on the printed wiring board 10. FIG. 4 (B)is an enlargement of a portion indicated by a circle b in FIG. 4 (A).

The solder resist layer 70 is formed on a surface of the printed wiringboard 10, and the connection pads 75 are formed to be exposed from theopenings 71 of the solder resist layer 70. Flux 79 is applied on theconnection pad formation region 75 g including the connection pads 75 ofone printed writing board 10. In the present invention, flux is appliedon each of the connection pads 75 except for contact portions betweenthe spacer 86 and the printed wiring board 10. Thus, an area where fluxis applied is smaller than an area of the opening portion of the spacer86.

For this reason, the flux is not attached on the spacer 86. Therefore,when the mask is detached from the printed wiring board, the printedwiring board need not to be inverted, and damage to the solder resistlayer 70 is reduced.

A case where the solder balls 78 are dropped on the connection pads 75,as in FIG. 4 (B), a height of the vertexes of the solder balls issubstantially flush with a height of a surface of the mask main body 82.According to the solder ball loading method of the first example, theheights of the solder ball 78 and the upper surface of the mask 80 aremade equal, to securely load a predetermined amount of the solder ballson the electrode pads 75, where each electrode pad 75 receives onesolder ball 78. This also reduces a probability that solder balls arenot loaded onto every electrode pad 75, or that a plurality of thesolder balls are loaded on a single electrode pad 75.

In the first example, the loading tube 24 is made of a conductive metalsuch as SUS stainless, Ni, and Cu, and the loading tube is grounded at aside of the solder ball loading apparatus 20. When the solder balls aremoved and carried on the ball alignment mask 80, the solder balls may beelectrically charged due to collision therebetween. However, solderballs having small diameter and light weight are not attached on theloading tube 24 electrostatically, and can be securely loaded on theprinted wiring board 10.

In the plan view of FIG. 18, a plurality of loading tubes 24 (althoughnot shown, the absorbed ball removing tubes 61 are also disposedsimilarly to the loading tubes) of the solder ball loading apparatus 20corresponding to each of the connection pad formation regions 75 g aredisposed on the sheet-sized multilayer printed wiring board 10A in the Ydirection. In this example one loading tube 24 corresponds to oneconnection pad formation region 75 g. However, the loading tube 24 maybe designed to have a size corresponding to a plurality of theconnection pad formation regions 75 g. Further, in this example the Ydirection is selected for the convenience of description. However, theloading tubes may also be disposed in the X direction.

The XYθ absorption table 14 of FIG. 11 positions, holds, and correctsthe multilayer printed wiring board's 10 position relative to where thesolder balls 78 are loaded. The alignment camera 46 detects thealignment marks of the multilayer printed wiring board 10 on the XYθabsorption table 14 and adjusts a positions between the multilayerprinted wiring board 10 and the ball alignment mask 80 based on thisdetected position. The solder ball detection sensor 18 detects theremaining amount of the solder balls 78 using an optical method.

Next, solder ball loading process using the solder ball loadingapparatus 20 is described with reference to FIGS. 12 to 14.

(1) Identifying and Correcting of Position of Multilayer Wiring Board

In FIG. 12 (A), alignment marks 34M of multilayer printed wiring board10A for gang printing are identified by the alignment camera 46, andposition of the multilayer printed wiring board 10A with respect to theball alignment mask 80 is corrected by the XYθ absorption table 14. Theposition of the printed wiring board 10A is adjusted so that theopenings 84 of the ball alignment mask 80 correspond to the connectionpads 75 of the multilayer printed wiring board 10A.

(2) Supplying of Solder Balls

Further, in FIG. 12 (B), the solder ball supplying apparatus 22 suppliesa predetermined amount of the solder balls 78 s to the side of theloading tube 24. Alternatively, the solder balls 78 s may be supplied tothe loading tube 24 in advance.

(3) Loading of Solder Balls

In FIG. 13 (A), the loading tube 24 is positioned over the ballalignment mask 80 while maintaining a predetermined clearance (forexample, 0.5 times to 4 times a diameter of the solder ball) to the ballalignment mask 80. Air is absorbed by the absorption portion 24 b, sothat an air flow rate at the gap between the loading tube and the ballalignment mask 80 is in a range of 5 m/sec to 35 m/sec. Accordingly, thesolder balls 78 s are collected on the ball alignment mask 80 disposedjust below the opening portion 24A of the loading tube 24.

Next, in FIGS. 13 (B), 14 (A), and 18, the loading tubes 24 that aredisposed along the Y axis of the multilayer printed wiring board 10A ofFIGS. 11 (A) and (B) are moved in a horizontal direction along the Xaxis by the X direction moving axis 40. Therefore, the solder balls 78 scollected on the ball alignment mask 80 are moved according to themoving of the loading tubes 24. The solder balls 78 s are thus loaded onthe connection pads 75 of the multilayer printed wiring board 10Athrough the openings 84 of the ball alignment mask 80. Accordingly, thesolder balls 78 s can be sequentially aligned on all of the connectionpads 75 of the side of the multilayer printed wiring board 10A.

(4) Removing of Attached Solder Balls

In FIG. 14 (B), redundant solder balls 78 s are induced by the loadingtubes 24 to positions of the ball alignment mask 80 where no openingsexist, and subsequently are absorbed and removed by the absorbed ballremoving tubes 61.

(5) Detachment of Board

The multilayer printed wiring board 10A is then detached from an XYθabsorption table 14.

According to the solder ball loading method of the first example, theloading tube 24 is positioned over the ball alignment mask 80, and airis absorbed by the absorption portion 24B (see FIG. 12 (B)) of theloading tube 24 to collect the solder balls 78 s. This is accomplishedby moving the loading tube 24 in the horizontal direction to move thecollected solder balls 78 s on the ball alignment mask 80. Then solderballs 78 s are dropped through the openings 84 of the ball alignmentmask 80 on the connection pads 75 of the multilayer printed wiring board10A. For this reason, fine solder balls 78 s can be securely loaded onall of the connection pads 75 of the multilayer printed wiring board10A. Further, because the solder balls 78 s are moved in a non-contactmanner, the solder balls are loaded on the connection pads withoutdamage, and the height of the solder bumps 78U is uniformly maintained.As recognized by the present inventors, a product manufactured accordingto the present invention exhibits good performance in mount-ability andan environment-resistance test when tested with ICs mounted. Examples ofsuch tests include heat cycle tests and high temperature/high humiditytests. Even in a case of a multilayer printed wiring board that hasunevenness on its surface, the solder balls 78 can still be securelyloaded on the connection pads 75 because the method described herein isindependent of product flatness. In addition, since the fine solderballs 75 s are securely loaded on the connection pads, and solder bumpshaving uniform heights can still be formed, even when a printed wiringboard has a connection pad pitch of 60 μm to 150 μm and a diameter ofopening of the solder resist of less than 150 μm.

Further, because the solder balls 78 are induced by the absorbing force,it is possible to prevent the solder balls from being agglutinated oradhered. Also, the number of loading tubes 24 can be adjusted, makingthe present invention adaptable to various sheet-sized multilayerprinted wiring boards 10A. Thus, the present invention can be used formulti-product, small-lot-sized production.

Example 2 (1) Manufacturing of Printed Wiring Board

A double-sided copper layered board (for example, MCL-E-67 manufacturedby Hitachi Chemical Co., LTD.) is used as a base material. Through-holeconductors and conductor circuits may be formed on the board by usingany well-known method. Next, interlayer insulating layers and conductorcircuit layers may be alternately laminated thereon using any well-knownmethod (for example, “Build-Up Multilayer Printed Wiring Board” writtenby Takagi Kiyoshi, published on Jul. 20, 2000 by NIKKAN KOGYO SHIMBUN,LTD), and connection pads for electrical connection to ICs is formed onthe outmost conductor circuit layer. Next, a solder resist layerincluding openings (for example, 150 μmΦ) is formed so as to expose theconnection pads.

(2) Loading of Solder Balls

(1) A commercially-available rosin-based flux is then applied onconnection pad formation regions of the manufactured printed wiringboard. Next, the printed wiring board is mounted on the aforementionedabsorption table 14 of the solder ball loading apparatus 20 according tothe present invention. The alignment marks of the printed wiring board10 and the ball alignment mask 80 are identified using a CCD camera, andthe printed wiring board and the ball alignment mask are aligned. Theball alignment mask 80 has a spacer on a rear surface thereof As theball alignment mask 80, a Ni mask having openings with a diameter of 110μm at positions corresponding to the connection pads of the printedwiring board is used. Although the Ni metal mask is used, othermaterials may also be used, such as a SUS or polyimide ball alignmentmask. It is preferable that a diameter of the openings formed on theball alignment mask 80 is 1.2 times to 1.5 times a diameter of thesolder ball used. Next, a SUS loading tube having a size (1.1 times to 4times a size of the connection pad formation region) substantiallycorresponding to the connection pad formation region and a height of 200mm is positioned over the metal mask (ball alignment mask) with aclearance of 0.5 times to 4 times a diameter of a solder ball. Forexample, Sn63Pb37 solder balls (manufactured by Hitachi Metals, LTD.)having a diameter of 80 μmΦ may be loaded on the peripheral ballalignment masks. Although Sn/Pb solders are used for the solder balls inthe Example 2, the composition of the solder balls is not limitedthereto, and any Pb-free solder selected from a group consisting of Snwith at least one of Ag, Cu, In, Bi, Zn, and the like may also be used.

Air is absorbed by the absorption portion (5 to 20 mmΦ)) 24B (see FIG.12 (B)) on the upper portion of the loading tube 24, to collect thesolder balls on the ball alignment mask 80 into the loading tube.

The loading tube 24 is then moved at a speed of 20 mm/sec, to move thesolder balls. The solder balls are dropped through the opening portionof the ball alignment mask, and loaded onto the connection pads. InExample 2, the loading tube 24 is made of a conductive metal such as aSUS stainless, Ni, and Cu, and is grounded at the side of the solderball loading apparatus 20.

After redundant solder balls on the ball alignment mask 80 are removed,the solder ball alignment mask 80 and the printed wiring board 10 areseparately detached from the solder ball loading apparatus 20.

The solder balls loaded on the connection pads are also subjected toreflow at a temperature of, for example, 230° C., to form predeterminedsolder bumps.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A solder ball positioning mask comprising: a mask main body includinga plurality of openings corresponding to a plurality of connection padson a printed wiring board, the plurality of openings being configured topass a solder ball through the solder ball positioning mask; a spacerincluding an opening portion configured to include the plurality ofopenings of the mask main body.
 2. A solder ball positioning maskaccording to claim 1, wherein the spacer is integrally formed on themask main body.
 3. A solder ball positioning mask according to claim 1,wherein a diameter of the plurality of openings on the mask main bodyranges from 1.2 times to 1.5 times a diameter of the solder ball.
 4. Asolder ball positioning mask according to claim 1, wherein the solderball positioning mask is made from any one of Ni, SUS stainless steel,and a polyamide material.